I will describe the necessary steps steps:
1) Download the new firmware from the official website
2) Open the settings by typing the modem address in the browser, for example, http://192.168.1.1 or 192.168.0.1 and enter the username/password.
3) In the interface that opens, open “System” – “Software Update”. On the page that opens, click “Browse” and select the previously downloaded new firmware file, then click “Update” to start the update process.
Wait for the update to complete, usually 2-5 minutes. At the end, the device will reboot.